Roller chains are used to transfer force from one rotating axle to an adjacent rotating axle. On a bicycle, a cyclist pushes pedals in a circular motion to rotate a center sprocket where a first portion of a roller chain is mounted. The second portion of the roller chain is mounted on a second sprocket mounted on the back wheel of the bicycle. As the first sprocket rotates, one portion of the chain, generally the top portion, is placed under strain and transfers the applied rotational force to the second sprocket and ultimately the back wheel. Roller chains in the mechanical industry work under the same principle. Chains can be reinforced by using larger links or by adding serial chains mounted on serial sprockets mounted on a drive axle.
Each link of a roller chain is placed cyclically under strain in one portion of the entire chain and released in the other portions of the chain. For example, in bicycles, the top portion of the chain is under strain while the bottom portion is free to hang under its own weight. As a result of this cyclical load, chains can be damaged by grinding wear. To minimize wear, friction must be reduced using use lubricants, rollers in or around the pins, or other systems such as intermediate sprockets to better distribute strain. Wear is any undesirable permanent mechanical degradation and ultimately leads a loss in efficiency and breakage. The measurement of wear in a roller chain is desirable to prevent breakage and to monitor and calibrate strain placed on chains.
Since roller chains are most often found with external links with two end pins and internal links end bushings inserted around the end pin of an external link, friction occurs mainly at the bushing/pin area. In a first type of wear, the pin is slowly damaged and its external radius is reduced. In a second type of wear, the bushing is slowly damaged and its internal radius is also reduced. In both of these instances of mechanical wear, the distance between two pins on the same external link remains unchanged, and the distance between two bushing on the same internal link also remains unchanged. The distance between adjacent external links and adjacent internal links increases gradually as wear increases in the bushing/pin area.
As the roller chain wears out, it becomes longer. Known methods in the art to measure wear include removing the chain from the sprockets to measure of a fixed length of chain with a ruler. This method has the obvious disadvantage of being imprecise and requires removing the chain from its operating position, which can be an extremely messy procedure, and having documented the original lengths of chain before wear occurs. Unworn chains with loose rollers can offset a ruler wear measurement.
Another technology used to measure wear is shown in U.S. Pat. No. 6,178,824 or in the marketplace as the Rohloff™ Caliber 2 or the Pack™ CC-3 Chain Checker. These devices are go/no-go gauges where one part of the tool is inserted around a first bushing at a heel and the tool is then rotated down. If the link is worn, a toe slides next to an adjacent bushing. These gauges are impractical to use, they are not adjusted for different sizes or models of chains, the tool to be slid in the chain opening cannot be located next to obstacles, and handles can obstruct measurement. These devices, due to their complex geometries, also are more prone to measurement error by unqualified operators. If the heel is not slid properly into position before the measurement is taken, the toe cannot “go” in a link, which results in a false negative.
Another technology is shown in U.S. Pat. Nos. 5,199,180 and 4,888,876 as long cylindrical or triangular telescoping sticks that are dropped inside the chain to measure wear. These multisectional devices also suffer inherent problems. First, wear gauge tools may need to be held in difficult orientations and positions to test the roller chains. For this reason, the telescoping system opened by gravity cannot measure from the underside of a chain. Gauges must also be as light as possible to obtain an unambiguous reading. The use of large handles or thick gauges is also problematic. In the case of telescopic gauges, if any of the segments of the gauge is partly unlocked, the operator obtains a false positive when the tip of the gauge does not slide into the chain but gives the impression of movement by retracting within the handle.
What is needed simple, light gauge capable of measuring wear of different sizes of roller chain with no chance of having false positive or negative measurements due to the operation of the gauge measuring a chain in any orientation or configuration.